1. Technical Field
The present invention relates to a heterocyclic compound and an organic light-emitting device including the same. More particularly, the invention relates to a fused ring compound, and to an organic light-emitting device that includes the compound.
2. Description of the Related Art
Organic light-emitting devices (OLEDs) are self-emitting devices having advantages such as wide viewing angles, good contrast, quick response speeds, high brightness, and good driving voltage characteristics. OLEDs can also provide multicolored images. Due to these characteristics, OLEDs have been receiving growing attention.
An existing organic light-emitting device has a structure that includes an anode disposed on a substrate, on which is sequentially stacked a hole transport layer (HTL), an emission layer, an electron transport layer (ETL) and a cathode. The HTL, the EML, and the ETL are normally formed of organic compounds. When a voltage is applied between the anode and the cathode, holes injected from the anode move to the EML via the HTL, and electrons injected from the cathode move to the EML via the ETL. The holes and electrons (carriers) recombine in the EML to generate excitons. When the excitons drop from an excited state to a ground state, light is emitted.
A major factor affecting luminescent efficiency of organic light-emitting devices is the organic luminescent material. Fluorescent materials have been widely used as organic light-emitting materials, but may have limited emission efficiency due to having a mere 25% probability of being in an excited singlet state. Meanwhile, phosphorescent materials have a 25% probability of being in an excited singlet state and a 97% probability of being in an excited triplet state, and thus may improve emission efficiency up to four times as compared with fluorescent materials (based on theoretical electroluminescence mechanisms), and may achieve a 100% internal quantum efficiency. Thus, use of phosphorescent materials is gradually increasing.
Anthracene derivatives are typical organic light-emitting materials. However, an organic light-emitting device using an anthracene derivative in which two or three oligomeric species of anthracene are linked by conjugation may have a narrow energy gap, low blue-light color purity, and low emission efficiency, and thus is not satisfactory.
4,4′-Bis(carbazole-9-yl)biphenyl (CBP) have also been used as a phosphorescent host material, but is not suitable for green-light emission due to its wide bandgap and reduced emission efficiency. It is also not easy to control hole or electron mobility and adjust the charge balance with this material.
These existing organic light-emitting materials do not yield satisfactory emission characteristics, such as emission efficiency.